Objective: The aim of this meta-analysis was to determine the effectiveness of neurofeedback treatments in adults with Attention Deficit/ Hyperactivity Disorder (ADHD).Methods: A total of 9 studies were selected, and meta-analysis was done on them. The data were gathered from the following databases: PubMed, ScienceDirect, Springer, SID based on methodological conditions, topic and research design, and the effect size of each study was calculated.Results: The combined effect size of all the indicators was found to be significant according to Cohen’s table, which means large or high effect size. The combined effect size for inattention is ES=0.0575 (P=0.0013), for impulsivity is ES=0.605 (P=0.0037), for hyperactivity is ES=0.545 (P=0.0384), for hyperactivity/impulsivity is ES=0.510 (P=0.001), and for total ADHD is ES=0.630 (P=0.0038).Conclusion: Based on the results of this meta-analysis, neurofeedback treatment was found to have a large effect in reducing ADHD symptoms in adults with attention deficit/ hyperactivity disorder.